While I don't burn oil yet, I have heard many say that you are best off getting an oil burner technician, and one who is familiar with evaporators, not just oil burners. They will have the knowledge to get the best boil rate/efficiency combination. A regular oil burner tech can get a good flame but they are not normally trained to get the best boil rate. It is not always just a matter of larger nozzle for more gal/hr evaporation. When the tech comes you will want a good amount of water for the test.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.